Railroad track circuits

ABSTRACT

A crossbond with a tuned circuit portion, matching the impedance of the rail circuit, is connected across the rails at each location between adjoining noninsulated track sections. A track circuit transmitter is so connected to each crossbond that its output divides equally between the tuned circuit and rail circuit paths. A hybrid coil arrangement couples a track circuit receiver to each crossbond, the coupling being so balanced between tuned and rail circuit paths that each receiver is responsive only to received rail current and not to output of collocated transmitter. All transmitters have a common output frequency for train detection, with each being approach controlled to supply cab signal current which also resets the track circuits after passage of a train.

United States Patent [72] Inventor Rayford C. Pace I-Iomewood, Ala. [211 App]. No. 828,198 [22] Filed May 27, I969 [45] Patented Apr. 20, I971 [73] Assignee Westinghouse Air Brake Company Swissvale, Pa.

[54] RAILROAD TRACK CIRCUITS 7 Claims, 2 Drawing Figs. [52] U.S.Cl 246/34(CT) 246/36 [5 I Int. Cl. B61] 23/30 [50] Field of Search 246/34, 34 I g 7 (CT), 36, 37, 35 [56] References Cited UNITED STATES PATENTS 3,328,581 6/1967 Staples Primary Examiner-Arthur L. LaPoint Assistant Examiner-George H. Libman Attorneys-H. A. Williamson, A. G. Williamson, Jr. and J. B.

Sotak ABSTRACT: A crossbond with a tuned circuit portion,

matching the impedance of the rail circuit, is connected across the rails at each location between adjoining noninsulated track sections. A track circuit transmitter is so connected to each crossbond that its output divides equally between the tuned circuit and rail circuit paths. A hybrid coil arrangement couples a track circuit receiver to each crossbond, the

Recoil/en 2 we en E5 [5 [I I RAILROAD TRMCIII CIRCUITS BACKGROUND OF THE INVENTION The invention disclosed herein relates to railroad track circuits. More particularly, my invention relates to an improved track circuit arrangement without insulated joints wherein current of the same frequency may be used for the detection of trains in adjoining track sections.

The use of noninsulated track circuits with high frequency or audiofrequency current in the rails is known in the railroad signaling art. Such arrangements use different frequencies in adjoining track sections in order to maintain a distinction between such adjacent circuits to avoid any extended overlap in their effective detection areas. It is also known that, if insulated joints are used between track sections, the same frequency current may be used without interference in adjoining track circuits. However, the use of insulated joints adds to the cost not only of installation, but of maintenance of any signaling system. At the same time, the requirement for a plurality of frequencies to distinguish between the noninsulated circuits has a major disadvantage of using up the available frequencies which may be needed for cab or train control signaling and for track circuits in parallel stretches of track. Thus a distinct advantage may be obtained with an arrangement by which rail current of the same frequency may be used for train detection in noninsulated sections, that is, even though insulated joints are not used between adjoining track sections. Such an arrangement obviously frees the remaining available frequencies for other purposes already listed.

Accordingly, an object of my invention is an improved railroad track circuit arrangement using the same frequency current for train detection in adjoining noninsulated track sections.

Another object of my invention is to provide a plurality of alternating current track circuits for a stretch of track without insulated joints, with all track circuit transmitters having a common frequency output for train detection purposes and each track circuit receiver so coupled to the rails as to be nonresponsive to a collocated transmitter.

A further object of my invention is a track circuit for a railroad track section using a hybrid coil arrangement to couple to the rails of the section a track receiver having a selected frequency response without the receiver being responsive to a collocated track circuit transmitter, for another section, having the same frequency output.

Still another object of my invention is an alternating current track circuit arrangement for a stretch of railroad track without insulated joints and divided into sections by crossbonds connected between the rails at selected locations, each such crossbond being tuned to match the rail input impedance for a track circuit transmitter connected thereto, a hybrid coil arrangement coupling a track circuit receiver to each bond and so arranged that no energy is supplied to that receiver from the hybrid coils as a result of their response to the output of the associated transmitter collocated at the same bond location.

Other objects, features, and advantages of this invention will become apparent from the subsequent specification and accompanying drawings.

SUMMARY OF THE INVENTION In practicing my invention, a crossbond with a tuned circuit portion matching the rail circuit input impedance is connected across the rails at each location dividing adjoining but noninsulated track sections. An alternating current transmitting means is connected to each crossbond in a manner that the tuned circuit portion and the rail circuit are in multiple across the transmitter so that its output current divides equally between these multiple circuit paths. All transmitters along a track stretch normally supply rail current signals of the same basic frequency for train detection but each shifts to signaling frequencies for cab signals or train control when the corresponding approach section becomes occupied. Track circuit receivers at each location are inductively coupled to the crossbond through a hybrid coil arrangement so positioned and interconnected, with respect to the transmitter connections, that the voltages induced in these hybrid coils by the output currents from the local, i.e., collocated, transmitter have no effect on the associated receiver. Only the hybrid coil voltages induced by current received through the rail circuits from transmitters at other locations are effective to energize the receiver at a particular location. A track relay controlled by receiver output normally sticks during the reception of detection frequency signals while the advance track section is not occupied. With occupancy of the advance track section, the track relay at a location releases to indicate train detection and to also establish a circuit for subsequently responding only to receiver output resulting from cab signal frequency current received when the advance section is again clear of any train. The train control frequency signals thus act as reset signals for the track circuit to restore the relay to its nonoccupied indication in I which it holds over the stick circuit.

RESUME OF THE DRAWINGS In each FIG. of the drawings, similar reference characters are used to designate similar parts of the apparatus.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT OF THE INVENTION Referring to FIG. I, there is shown across the top of the drawing a stretch of railroad track illustrated in a conventional manner by a single line for each rail, designated at the left by the reference characters 11 and 12. For convenience in the following description, it is assumed that train movements in this stretch of track are from left to right. However, from the description, it will be obvious that control of two direction movement of trains is possible using the track circuit arrangement of my invention modified in a conventional manner by well known traffic control principles of railroad signaling. This stretch of railroad track is divided into sections at locations D, E, and F. Portions of the'track stretch between these locations are hereinafter defined as track sections and are designated in the drawing as sections IT at the left, 3T between D and E, 5T between E and F, and 7T at the right. Sections IT and 7T, of course, are not fully shown. These track sections are not separated by insulated joints in the rails and therefore each rail is a continuous conductor throughout the stretch shown. One advantage immediately results from such an arrangement in electric propulsion territories, for example, a rapid transit system, in that the usual return circuit path through the rails for propulsion current is therefore readily available without the use of special impedance bonds around any insulated joints.

Each of the designated locations between adjoining sections is specifically marked by an electrically conductive crossbond connected between the rails at that point. For example, crossbond CBE is connected between the rails at location E. Each of these crossbonds includes a circuit portion having, in parallel, inductive and capacitive elements, the details of such arrangement being discussed shortly in connection with FIG. 2. Connected directly to each crossbond is a track circuit transmitter unit, such as unit T3 at location E, and coupled to each crossbond is a collocated track circuit receiver unit such as unit R5 at location E. The details of these direct connections or couplings of the transmitters and receivers,

respectively, will be described in detail shortly, also in connection with FIG. 2.

Each transmitting unit is operable when supplied with an input voltage of a preselected frequency to transmit to the rails sufficient energy of that frequency to provide rail current in the track sections for train detection or for inductive reception by train carried control apparatus, in a well known manner. However, in each of the drawings, the transmitter units are shown by a conventional block, appropriately labeled, as the specific details of these transmitters are not a part of my invention and any available arrangement which will provide the described operation may be used in the illustrated system. Each transmitter is also designated by a reference T with a numerical suffix corresponding to the approach section. Referring particularly to transmitter unit T3 at location E in FIG. l, it is supplied with an input voltage, having a basic or train detection frequency fl, over front contact a of a track relay repeater 3TP, which will be fully described later. This is the normal condition when no train is occupying the stretch of track. At other times, relay 3T? releases so that the input terminal of transmitter T3 is connected over back contact a of relay 3TP to the annature of contact c of track relay STR. As will be discussed later in detail, this occurs when a train occupies the approach track section 3T to location E. Track relay ST R is defined as the local location, that is, location E, track relay for train detection in the advance track section 5T. Depending upon the position of relay STR when relay 3TP releases, energy having a frequency f2 or f3 is supplied to transmitter T3. As will be subsequently described, energy at frequencies 12 and f3 is used primarily to provide cab signal or train control current or signals in the rails for purposes of controlling the safe operation of the trains traversing the stretch of track. However, this specific energy supply is also used to reset the track circuit apparatus after a track occupied condition (for section 5T) has occurred and thus at least frequency f3 is at times defined as a reset frequency.

Energy having the frequencies fl, f2, and f3 may be supplied to all locations from common generators, one for each frequency, located at a single point and connected over wayside line wires to the various locations. Preferably frequency fl energy is so supplied in order to avoid interference due to phase differences in the overlapping output of the various transmitter for train detection purposes in the noninsulated track circuits. Phase relationship of the rail signals at frequencicsjZ and f3 is not critical and therefore this energy may, if desired, be supplied by local oscillators at each wayside location. As an example, the common supply of energy at frequency fl may extend between interlocking locations along the stretch of track where insulated joints are used for other control purposes. In the drawings, connection to the common or local energy source of any of these frequencies is shown, for convenience, merely by a terminal designated by the corresponding frequency reference character.

Each of the receiver units is likewise shown in the two drawing FIGS. by a conventional block, appropriately labeled, since again the details of such units are not a part of the inventive concept of this arrangement. Such receiver units are tuned to be selectively responsive to the reception of current signals from the rails having a frequency fl or a frequency 13. Each receiver is provided with a common output terminal x, a second output terminal fl activated only when current has the frequency 13. Each receiver unit R controls an associated track relay TR, such as relay 5T R controlled by receiver R5 at location E. The basic reference character for each receiver and associated track relay have numerical suffixes or prefixes, respectively, corresponding to the numerical designation of the advance track section at that location. When section ST is unoccupied by a train and the track circuit system is completely reset, relay STR is energized by a stick circuit traced from output terminal fl of receiver R5 over front contact a and the winding of relay 5T R, returning to the common terminal x of receiver R5. When section ST is occupied by a train and, as subsequently described, all outputs from receiver R5 cease, relay STR releases and shifts its control circuit so that the winding of relay STR is connnected over its back contact a to output terminal 13 of receiver R5, the other terminal of the relay winding remaining connected to the common output lead of the receiver. When section ST is again clear of train occupancy, relay STR must be reenergized through receiver R5 by the reception of rail current signals at frequency f3, under these conditions being used as reset energy for the track circuit.

Each track relay TR controls, over a line wire, a front contact repeater relay at the next location in advance. For example, track repeater relay STP at location F is controlled by a circuit extending between terminals B and N of a direct current source (not shown) over front contact b of relay STR and a line wire connection 13 between the two locations. Obviously, relay 5T P repeats the operation of relay STR, normally repeating its picked up condition and releasing, when track section ST is occupied by a train,.in response to the release of relay STR to interrupt the energizing circuit.

Referring now to H6. 2, I shall explain the operation of the crossbond circuit connections which are illustrated in somewhat greater detail in this FIG. HO. 2 shows a typical location between adjoining track sections, such as any one of the locations D, E, and F of FIG. 1. A typical crossbond CB is connected between rails ll and 12, each shown here by a double line symbol. The physical configuration of crossbond CB as specifically shown in FIG. 2, and in FlG. l, is a matter of convenience in illustrating the circuits and is not limiting as to the actual physical arrangement of such apparatus. Only the defined electrical characteristics of the crossbonds as herein described are pertinent to the novelty of my invention. it is to be noted that crossbond CB includes a circuit portion having an inductor L and a capacitor C connected in multiple. The inductance provided by L may be an inherent part of the crossbond itself, but preferably such inductance is provided by a coil having one or, at most, only a few turns. This parallel L-C circuit portion of the crossbond is tuned to match the input impedance of the rail circuit to which the crossbond is connected.

The output connections of the associated track circuit transmitter at the location are so arranged that the tuned L-C circuit portion of the crossbond and the rail circuit are in multiple across the transmitter output. Since the tuned circuit portion matches the impedance of the rail circuits, the output of the transmitter thus divides equally between the two multiple circuit paths. This is illustrated by the dotted arrows in FIG. 2 which designates an instantaneous current flow from the 7 location transmitter through the track circuit arrangement. In other words, the output current of the track circuit transmitter divides so that one part flows through the parallel L-C circuit portion of crossbond CB while an equal part of the output current flows through the remainder of the crossbond into one rail and returns from the other rail to the transmitter. Obviously, since there are no insulated joints at a particular location, that portion of the transmitter output reaching the rails divides between the adjoining track section rail circuits but this does not limit my inventive concept. Also shown in FIG. 2, between the transmitter and its track circuit or crossbond connections, is a matching or isolation transformer MT which is a preferable arrangement for such connections. It is illustrated specifically in FIG. 2 but not shown in FIG. 1 since preferably the matching transformer will be an integral part of the transmitter unit so that an additional item of apparatus does not have to be connected into the arrangement.

The receiver unit at each location is coupled to the crossbond through a hybrid coil arrangement so as to respond only to current from the rails, that is, to energy signals received from other than the associated transmitter at the same location. An instantaneous flow of current from the rails through crossbond CB is illustrated by the solid line arrows in FIG. 2. It is apparent that the current entering the crossbond from rail l l flows entirely through the crossbond including the tuned circuit portion and out into rail 12. The minor part flowing through the primary of transformer MT may be ignored. In FIG. 2, the hybrid coils M, N, O, ,and P coupling the receiver to the crossbond are shown schematically in sufficient detail to illustrate the polarity of the induced energy from the rail current, based on the well known right-hand rule. The equivalent output terminal of each coil is then marked by a conventional heavy dot symbol. Further, these hybrid coils are interconnected so that a like polarity output in each coil adds to produce a final output from the hybrid arrangement to the receiver. Although a more or less conventional four coil hybrid arrangement is illustrated, it will be understood that any balanced coil arrangement having a different number of coils may be used to produce the results next described.

Considering again the specific arrangement illustrated, since current from 'the rails flows in the same direction through the crossbond at each of the hybrid coils, the instantaneous induced voltage from such rail current produces a like polarity in each hybrid coil, for example, positive at the dot symbol. The individual coil outputs thus add, causing the application of energy to the associated receiver. However, the output current from the associated transmitter at that location flows in opposite direction through each pair of coils, as illustrated by the dotted current arrows. Therefore, the output of each pair of coils, that is, M and N, and O and P, is of opposite polarity so that cancellation of the induced energy occurs and there is no resulting output into the associated receiver due to the flow of energy from that collocated transmitter. Thus the output of the transmitter at a particular location has no effect on the associated receiver unit. Said in another way, a receiver unit at a location responds only to current received through the rails from transmitters at other locations. It may be noted that, when no trains are in the stretch, the rail current flowing in a particular crossbond is actually supplied by transmitters at least at the locations next adjacent in each direction.

I shall now describe the operation of the track circuit arrangement embodying my invention with reference particularly to FIG. 11. It may be noted that the coupling coils as illustratedin this FIG. in connection with each crossbond CB are shown conventionally but the equivalent instantaneous output terminals are marked, as in H0. 2, with a conventional heavy dot. Each crossbond CB and its corresponding inductor L and capacitor C are distinguished by adding to the conventional reference character a suffix letter the same as that designating the location. initially in the description, it will be assumed that no trains are occupying any portion of the stretch of railroad track shown.

Under the assumed condition, all track relays are energized and picked up. For example, relay TR is energized by the circuit, including its own front contact a, connected across terminals x and fl of receiver R5. Likewise, all repeater relays T? are energized over front contact b of the corresponding track relay in a direct repeating circuit. All track circuit transmitters are supplying current of frequency fl to the rails since, at each illustrated location, front contact a of the track repeater relay TP is closed. As described, the output of transmitter T3, for example, is connected to crossbond CBE and divides equally between the rail circuits across which the crossbond is connected and the matching impedance circuit portion of bond CBE including inductor LE and capacitor CE. Under these conditions, the energy induced in the hybrid coils coupled to bond CBE by the output of unit T3 cancels and there is no resulting output to be supplied to receiver RS. Rather, this receiver receives energy through the hybrid coil coupling as a result of the current flowing through crossbond CBE from the rails and actually supplied by transmitters Ti and T5 at the adjacent location.

it is now assumed that a train approaches through track section 11'! and passes location D to enter section 3T. The shunt across the rails provided by the wheels and axles of the train removes all supply of energy at frequency fl from receiver R3 at location D, in particular such energy at this frequency as is then being received through the rails from transmitter T3 at location E. RElay 3TR is thus deenergized and releases to detect the occupancy of section 3T by the train. The opening of front contact b of relay 3TR obviously deenergizes its repeater relay 3TP. This latter relay releases to transfer the input energy for transmitter, T3 from the frequency fl supply source to a supply of energy at frequency f2 over front contact c of relay STR. Frequency f2 is specifically associated with the cab signal or train control apparatus carried by the train and such signals are received by the train carried apparatus in a well known manner to provide a proceed signal or normal speed control for that train as it moves through section 3T. This supply of train control energy to section 3T is thus approach controlled to occur only when a train enters that section and its occupancy or presence is detected through the combined release of relays 3TR and 3TP. The release of relay 3TR to open its front contact c and close the corresponding back contact shifts the train control energy supplied to the rails of section llT from frequency f2 to frequency f3. Thus any following train entering section 1T will receive a restricted train control signal allowing it to proceed only at a slow speed prepared to stop short of location D.

When this assumed preceding train enters section 5T upon passage of location E, relay STR is released by the train shunt across the rails which cuts off all energy at frequency fl being supplied through the rails from transmitter T5 at location F. Relay STR releases to apply energy at frequency f3 over its back contact 0 to transmitter T3. AT the same time, relay STP is deenergized by the opening of front contact b of relay STR and releases to apply train control energy of frequency f2 to transmitter T5, at the same time removing the supply of energy of frequency fl from this transmitter and thus from the rails of section ST. The train thus continues to receive train control signals allowing it to proceed through section 5T at normal speed.

When this train clears section 3T, that is, the rear end passes location E, the rail shunt is removed and the output of transmitterT3 is again applied through the rails of section 3T to location D. As previously explained, this flow of current at frequency f3 from transmitter T3 is not effective, due to the hybrid coil arrangement and the matching impedance portion of crossbond CBE, to energize relay STR through its associated receiver R5. At location D, however, current of frequency 13 is applied to receiver R3 through the hybrid coil arrangement and in turn energizes relay 3TR which at this time is connected over its back contact a across common terminal x and terminal f3 of receiver R3. Relay 3TR picks up, closing its front contact b to reenergize relay 3TP at location E. This latter relay, at its contact a shifts the supply of energy to transmitter T3 from frequency f3 to frequency fl. At the same time, relay 3TR has closed its front contact a to connect its winding across output terminals fl and x of receiver R3 so that it will respond to the reception by receiver R3 of rail current signals of this frequency from location E. in engineering a specific installation relay 3TR may be required to have slow release characteristics in order to bridge the shift of the current supply from frequency 13 to frequency fl by the pickup of relay 3TP. When relay 3TR picks up, its contact c shifts the supply of energy to transmitter Tl from frequency 13 to frequency f2, if relay lTP is released. Thus any following train approaching through section 1T will now receive train control or cab signal energy allowing it to proceed at normal speed through that section.

It is to be noted that, while the first train was occupying any part of section 3T, relay 3TR at location D does not pick up regardless of any output provided by transmitter T1 to the rails of section lT. This results from the arrangement of the hybrid coils coupled to crossbond CBD. Thus the train occupying section 3T is protected from the approach of any following train through section lT since this following train will receive speed control signals that require it to stop short of location D. Similarly, while the preceding train is occupying section 5T, the following train may enter section 3T so that relay 3TR again releases to detect its occupancy of that section. However, with relay STR released, the release of relay 3TP, repeating the action of relay 3TR, results in the application to unit T3 of train control energy of frequency f3 over back contact of relay T R and back contact a of relay 3TP. Thus the following train must approach location E prepared to stop and the preceding train remains protected from a following movement. It is also to be noted that, if there is no closely following train so that relay IT! is picked up and the output of transmitter T1 is thus at frequency fl, relay STR cannot pick up even through receiver R5 receives frequency fl energy from the rail current through section 3T. Since relay 5T R released when the train entered section 5T, it is conditioned by the circuit over its back contact a to respond only when receiver R5 receives energy at frequency f3.

Relay 5T R, once the preceding train has cleared section 5T, with or without a following train, is reset in a manner similar to that just described for relay 3TR. ln other words, signals of frequency 13 are received by receiver R5 which in turn energizes relay STR over its back contact a. This relay picks up, closing its front contact b to reenergize relay 5T P. At the same time, relay STR closes its own front contact a to complete a stick circuit so that it will remain picked up when rail current of frequency fl replaces that of frequency )3, due to the closing of front contacta of relay STP.

This track circuit arrangement of my invention also guards against the consequences of a broken rail since such will be detected prior to the arrival of a train within that section. Assuming that a rail within section 5T has broken, the track or rail circuit is interrupted and track circuit energy at frequency fl from transmitter T5 is cut off from receiver R5. If no trains are initially anywhere within the illustrated stretch, sufficient energy from transmitter T1 at location D will be received, however, by receiver R5 to retain relay STR initially picked up. When an approaching train occupies section lT, resulting in the release of relay lTP, the shift to a supply of energy at frequency 12 to the rails of sections IT and 3T by transmitter Tl will cause relay 5T R to release since no energy of frequency fl is now being received by receiver R5. As soon as the train enters section 3T and relays 3TR and 3TP release, with relay 5T R already released only train control energy of frequency 13 is supplied to transmitter T3, over the circuit including back contact c of relay 5T R and back contact a of relay 3TP. Transmitter T3 can thus only supply a restricted speed signal to the train approaching through section 3T. This train is then required to stop short of location E and obtain special permission from the dispatcher, or wait the repair of the broken rail, before it can proceed at any speed through section 5T. Thus the train is protected against the consequences of the broken rail in section ST.

The track circuit arrangement of my invention thus allows the use of a single or common frequency for train detection in successive noninsulated track sections throughout a stretch of railroad track. Other frequencies of the limited number normally available for such systems can then be used for train control purposes in the same track sections, or in parallel tracks for train detection, without interference between the various uses. At the same time, the safety requirements of railroad signaling systems are not sacrificed in any degree. An efficient and economical track circuit system thus results from the use of the features and advantages provided by this novel system of my invention.

While I have described above the principles of my invention in connection with a single embodiment of apparatus including the invention, it is to be understood that this description is made by way of example only and not as a limitation to the scope of my invention, as various modifications and changes within the inventive scope will be apparent to those skilled in the art of railroad signaling.

I claim:

1. ln a stretch of railroad track divided at predetermined locations into a plurality of noninsulated track sections, a

track circuit arrangement for detecting trains occupying particular sections, comprising in combination,

a. an electrically conducting crossbond at each location, connected between the rails and including a tuned circuit portion matching the input impedance of the rail circuit path adjoining that location.

. signal transmitting apparatus at each location operable to provide rail signals normally of a common detection frequency and at other selected times of a common reset frequency,

l. each transmitting apparatus connected to the associated crossbond to supply its rail signals in multiple equally to said tuned circuit portion and said rail circuit path,

c. a track receiver at each location coupled to the associated crossbond in such manner as to respond only to signals received through the rail circuit path from transmitting apparatus at other locations,

I. each receiver responsive to the received rail signals to produce a first or a second output signal as the received signals have said detection frequency or said reset frequency, respectively, and

d. a track relay at each location normally connected to the associated track receiver to be held energized by the receiver first output signal when the advance track section is nonoccupied and releasing when a train occupies that advance section,

I. each track relay when released connected to the associated receiver to be energized by the receiver second output signal when a train vacates the advance track section,

2. each track relay,controlling the adjacent advance location transmitting apparatus to provide rail signals of said detection frequency or of said reset frequency as that track relay is energized or released, respectively.

2. A track circuit arrangement as defined in claim 1, further including a hybrid coil arrangement at each location coupled to the associated crossbond,

a. each hybrid coil arrangement being interconnected for canceling signals induced therein by the rail signal output of the associated collocated signal transmitting apparatus and for summing signals induced therein by rail signals received through the rail circuit path from signal transmitting apparatus at other locations,

b. the track receiver at each location connected to the corresponding hybrid coil arrangement for responding to rail signals received from the signal transmitting apparatus at the adjacent advance location to provide a first or second output signal only when rail signals are received through the rail circuit path.

3. A track circuit arrangement as defined in claim 2 in which each said hybrid coil arrangement includes,

a. a selected number of windings inductively coupled to the tuned circuit portion of the associated crossbond, and

b. an equal number of windings inductively coupled to the rail circuit portion of said associated crossbond,

c. all said windings being so interconnected that the sum of signals induced in the windings coupled to said tuned circuit portion are of opposite polarity and equal value to the sum of those signals induced in the windings coupled to said rail circuit portion, when rail signals from only the collocated transmitting apparatus fiow in the associated crossbond. v

4. A track circuit arrangement as defined in claim 3, in which said reset frequency signals also provide signals for controlling the movement of a train approaching a location.

5. A track circuit arrangement as defined in claim 4 in which said transmitting apparatus at each location is controlled by,

a. the track relay at the adjacent approach location for supplying said common detection frequency signals when the approach track section is nonoccupied and for manner as to an occupied condition of that section when a train occupies the approach section for protecting the movement of that approaching train.

7. A track circuit arrangement as defined in claim 5, in which each track relay is connected to the associated track receiver over its own energized position and over its own released position contact to receive the first and second output signal, respectively, of that receiver. 

1. In a stretch of railroad track divided at predetermined locations into a plurality of noninsulated track sections, a track circuit arrangement for detecting trains occupying particular sections, comprising in combination, a. an electrically conducting crossbond at each location, connected between the rails and including a tuned circuit portion matching the input impedance of the rail circuit path adjoining that location. b. signal transmitting apparatus at each location operable to provide rail signals normally of a common detection frequency and at other selected times of a common reset frequency,
 1. each transmitting apparatus connected to the associated crossbond to supply its rail signals in multiple equally to said tuned circuit portion and said rail circuit path, c. a track receiver at each location coupled to the associated crossbond in such manner as to respond only to signals received through the rail circuit path from transmitting apparatus at other locations,
 1. each receiver responsive to the received rail signals to produce a first or a second output signal as the received signals have said detection frequency or said reset frequency, respectively, and d. a track relay at each location normally connected to the associated track receiver to be held energized by the receiver first output signal when the advance track section is nonoccupied and releasing when a train occupies that advance section,
 1. each track relay when released connected to the associated receiver to be energized by the receiver second output signal when a train vacates the advance track section,
 2. each track relay controlling the adjacent advance location transmitting apparatus to provide rail signals of said detection frequency or of said reset frequency as that track relay is energized or released, respectively.
 2. A track circuit arrangement as defined in claim 1, further including a hybrid coil arrangement at each location coupled to the associated crossbond, a. each hybrid coil arrangement being interconnected for canceling signals induced therein by the rail signal output of the associated collocated signal transmitting apparatus and for summing signals induced therein by rail signals received through the rail circuit path from signal transmitting apparatus at other locations, b. the track receiver at each location connected to the corresponding hybrid coil arrangement for responding to rail signals received from the signal transmitting apparatus at the adjacent advance location to provide a first or second output signal only when rail signals are received through the rail circuit path.
 2. each track relay controlling the adjacent advance location transmitting apparatus to provide rail signals of said detection frequency or of said reset frequency as that track relay is energized or released, respectively.
 3. A track circuit arrangement as defined in claim 2 in which each said hybrid coil arrangement includes, a. a selected number of windings inductively coupled to the tuned circuit portion of the associated crossbond, and b. an equal number of windings inductively coupled to the rail circuit portion of said associated crossbond, c. all said windings being so interconnected that the sum of signals induced in the windings coupled to said tuned circuit portion are of opposite polarity and equal value to the sum of those signals induced in the windings coupled to said rail circuit portion, when rail signals from only the collocated transmitting apparatus flow in the associated crossbond.
 4. A track circuit arrangement as defined in claim 3, in which said reset frequency signals also provide signals for controlling the movement of a train approaching a location.
 5. A track circuit arrangement as defined in claim 4 in which said transmitting apparatus at each location is controlled by, a. the track relay at the adjacent approach location for supplying said common detection frequency signals when the approach track section is nonoccupied and for supplying selected train control frequency signals when a train occupies said approach section, and b. the associated track relay for selecting a first train control frequency when the advance track section is nonoccupied and a second train control frequency when said advance section is occupied by a train, said second train control frequency being also the reset frequency.
 6. A track circuit arrangement as defined in claim 5 in which said track receiver at each location is responsive to a broken rail condition in the advance track section in the same manner as to an occupied condition of that section when a train occupies the approach section for protecting the movement of that approaching train.
 7. A track circuit arrangement as defined in claim 5, in which each track relay is connected to the associated track receiver over its own energized position and over its own released position contact to receive the first and second output signal, respectively, of that receiver. 